what does ::eqref:eq_matrix_def represents in 2.3. Linear Algebra?

It is just the matrix A definition, the 2.3.2. There is a texting editing issue with that tutorial.

what does ::eqref:eq_matrix_def represents in 2.3. Linear Algebra?

It is just the matrix A definition, the 2.3.2. There is a texting editing issue with that tutorial.